Terrestrial Biodiversity Adaptation Research Network

Can 'geoengineering' protect ecosystems and humanity from climate change impacts, should global warming start to run out of control? Well, not really, say Lunt and co-authors, in a fascinating application of a Global Climate Model (HadCM3L) that poses the ultimate 'what-if?' scenario for a human response to climate change. The situation they model is the speculative idea that we could install roughly a trillion 1m diameter reflective mirrors between the Earth and the Sun, to reduce incoming solar radiation by 2-5%. Costs and logistics aside, would this mitigate climate change impacts? The answer is complex, but the upshot is that such a geoengineering solution-of-last-resort would seem to create as many problems as it solves. The tropics would cool, which might spare rain forest biomes or cause them to revert to savanna, but polar amplification of the warming is predicted to continue, leading to the elimination of Arctic sea ice and the probable continued destabilisation of land-based polar ice sheets. This solution could avoid major heat waves that threaten coral reef systems with bleaching. The global hydrological cycle would likely become less intense, with the atmosphere being drier overall. However, ocean acidifiction due to high CO2 would be unaffected by this geoengineering, and this impact alone is likely to be catastrophic for species such as corals, forams and pteropods that secrete a calcite or aragonite skeleton, potentially disrupting entire strands of the marine food web. Interestingly, the authors speculate that the sort of conditions implied by this scenario (lower total solar irradiance and high atmospheric CO2 concentration) would have the side effect of re-creating a world similar to the Cambrian period, 500 million years ago - the dawn of the Phanerozoic Era, when visible life first became abundant on the planet.

Lunt DJ, Ridgwell A, Valdes PJ, Seale A (2008) 'Sunshade World': A fully coupled GCM evaluation of the climatic impacts of geoengineering. Geophysical Research Letters 35:L12710, doi:10.1029/2008GL033674

From: South Australian Government, Premier's Climate Change Council, Expert Science Subgroup